The invention generally relates to optical projectors for producing color images on screens in response to tri-color pixel image data. More particularly, the invention concerns an optic engine architecture, a polarization technique and an overall configuration for such optical projectors that represent significant improvements in image quality, durability and portability.
Conventional optical projectors have a horizontal form factor that produces a relatively large footprint or horizontal outline on the stand, table or support surface. The image is projected from such prior art projectors from a height that is very few inches above the support surface, whereas the screen or display surface is at a substantially higher elevation so that it is easily viewable by persons in a conference room or lecture hall. Such upward image projection systems suffer from a well-known phenomenon called Keystone distortion. Conventional projectors tend to be bulky and barely portable, by which is meant they typically are transported on a wheeled cart because they cannot be comfortably handcarried by the average person. Finally, conventional projectors require a fair amount of preventive and corrective maintenance of their optics engines, or modules, because of their relative fragility and tendency to be jarred out of alignment from normal use.
The invented optics engine uses a prismatic cube for color separation or beam splitting, with the prismatic elements within the cube being secured within a durable frame that mounts three monochrome light valves, e.g. twisted nematic liquid crystal display (LCD)-type shutters, in a predefined position and orientation relative to the prismatic cube. In order to improve image quality and brightness, especially of the notoriously difficult-to-reproduce green color, red and blue beams are S-polarized, as is conventional, but the green beam is P-polarized. Edge jitter in all three colored beam paths is minimized preferably or eliminated by guard banding thereagainst by polarizer design, e.g. by selection of polarizer plane and bandpass characteristics.
The invented optical projector preferably includes a frame having a footing portion for resting on a support surface, a light source high above the footing portion, optical convolution structure downstream from the light source for reverse-bending downwardly flowing light from the source, light modulation structure near the reverse bend region for infusing the light with image information and for propelling modulated light upwardly in a projectable, image-containing stream of light, and outward-projection directing structure high on the frame for receiving and outwardly directing such stream of light. This optical projector structure, in its preferred embodiment, has a tower-like configuration, with a small footprint, and a very lightweight, yet durable, construction having high image quality including brightness.
These and other objects and advantages of the invention will be more clearly understood from a consideration of the accompanying drawings and the following description of the preferred embodiment.